Paper B shows how to choose and size a ventilator battery: comparing NiMH against lithium-ion for a high-rate, life-support load, fixing the voltage architecture, working the energy calculation at worst-case breath settings, and specifying the construction details that let a pack deliver blower power reliably for years.
Lithium-ion (often high-voltage multi-cell packs for blower-driven systems) wins on weight and energy per kilogram, which matters for handheld EMS ventilators — at the cost of a mandatory BMS, precise charge control and a flammable electrolyte whose safety must be engineered. NiMH is heavier but intrinsically safe (aqueous electrolyte, extremely low thermal-runaway risk), tolerant of prolonged float at the bedside and of overcharge with proper termination, high-rate capable, and degrades gradually. For ICU ventilators that live docked at a bed and for rugged transport platforms where safety margin beats grams, NiMH remains a defensible, field-proven selection.
A high-speed blower needs a bus voltage high enough to sustain peak inspiratory flow at end-of-discharge. Designs use either a nominal 12–14.4 V rail (10–12 NiMH cells, or 3–4 Li cells) or a higher 24–48 V rail in larger turbine systems. The series count is validated at the worst corner: aged cells, low state of charge, maximum pressure-support breath, cool ambient — the point where bus voltage must still keep the blower in control. A DC/DC stage cannot manufacture power from a collapsed pack.
Suppose a transport ventilator averages 25 W over a worst-case breath pattern and the clinical requirement is 2 hours of internal operation plus a 25 % delay margin: energy demand is 25 W × 2.5 h = 62.5 Wh. On a 12 V NiMH rail that is about 5.2 Ah raw; depth-of-discharge (0.85), end-of-life fade (0.8) and a temperature margin (0.85) raise the design capacity to roughly 9 Ah. The same calculation at a nominal easy setting would under-size the pack by a third — precisely the error that causes field complaints of "short battery" alarms in difficult patients.
Blower current is delivered breath after breath for millions of cycles, so pack construction is decisive: matched cells by internal resistance (not just capacity), thick welded busbars sized for peak current, low-impedance protection that never nuisance-trips on an inspiratory surge, and thermistors placed on cells rather than casing. Heat from repeated high-rate discharge accelerates NiMH aging, so the mechanical design must give the pack a thermal path away from the blower and power electronics.
ICU ventilators float on charge between uses; NiMH accepts this with -ΔV/temperature-terminated charge followed by maintenance trickle, staying indefinitely ready without the calendar-stress concerns of a lithium cell held at full voltage at elevated temperature. Charge time to the manufacturer-declared readiness level should be validated with the device powered on, as clinicians recharge between transports rather than in a workshop.
Weijiang Power builds high-rate, matched NiMH packs for respiratory OEMs with IEC 62133-1 and UN 38.3 documentation, welded busbars, NTC supervision and connectorised assemblies. Send your worst-case settings, declared internal endurance and rail voltage and we will size and validate the pack to sustain essential performance.
